This invention relates to a tubular member having fluid flow control means positioned on the inner wall surface thereof operable for purposes of effecting control over the movement of fluid flowing through the tubular member, and more particularly, to an electrical circuit employable in cooperative association with welding means for purposes of effecting the application of the aforesaid fluid flow control means on the inner wall surface of the tubular member.
It is widely known that a major operating component of any conventionally constructed steam generation system is the boiler. Likewise, it is widely known that it is in the boiler that the generation of steam is actually effected. In this regard, the aforesaid generation of steam is commonly accomplished as a consequence of the passage of water through a multiplicity of tubular members, i.e., tubes, during the passage of which the water is sufficiently heated so as to cause it to change state, i.e., to change from liquid to a vapor.
Within a heat transferring or vapor, i.e., steam, generating system, there exists an infinite number of conditions relating to temperature, primary and secondary fluid movements, and structural configurations that influence the performance thereof. Accordingly, it is both desirable and beneficial to have the capability to design into such systems precise and accurate control of the fluid movement therewithin so as to maximize the efficiency of the system.
In this regard, there can be found set forth in copending patent application Ser. No. 73,967, which was filed on Sept. 10, 1979, now U.S. Pat. No. 4,314,587 and which is assigned to the same assignee as the present invention, a boiler tube that is provided on the inner surface thereof with the physical characteristics that are required thereby in order to insure the existence of a proper fluid movement therethrough, i.e., so that the heat transfer rate to the fluid medium is maximized. In accord with the teachings of the aforesaid copending patent application, the tube bore surface is made uneven such as, for instance, by deforming the existing tube material, or by affixing additional material thereto as through the welding thereof, or by depositing weld metal thereon. Such modifications of or additions to the material that constitutes the tube bore surface is intended to function to provide a turbulence to the fluid thereby tending to eliminate a temperature gradient within the fluid at any cross sectional plane taken across the tubular area. In addition, this exercise of control over the fluid motion within the tube is also intended to function to prevent the formation of vapor pockets or vapor layers adjacent to the tube inner wall surface that operate to provide an adverse effect on the heat transfer properties of the medium.
Obviously, it is important that boiler tube failure be avoided in steam generating systems. Moreover, one cause of boiler tube failure is known to be that of overheating of the tube. Furthermore, it is known that an inefficient transfer of heat through the tube wall to the water, i.e., fluid medium, flowing therewithin can lead to the tube overheating. The reference here to an inefficient transfer of heat through the tube wall is meant to encompass the situation wherein the accomplishment of the desired heat transfer process is impeded by the presence of so-called nucleate boiling, i.e., wherein stagnation of steam bubbles that function in the nature of insulation impedes the passage of the heat through the tube wall to the water flowing therewithin.
To summarize, the condition, which is sought to be avoided here in an effort to minimize the susceptibility of the tube becoming overheated as a result of nucleate boiling, is that wherein there exists within the tube a laminar flow of water or steam. As used herein, the term laminar flow is meant to refer to a streamline or viscous flow of the fluid axially of the tube. Namely, what is desired is the effectuation of the breaking up of such laminar flow in the tube.
As the water flows through the tube, the outer layer of the water, i.e., the layer of water in closest proximity to the inner wall of the tube, becomes heated by the heat being transmitted through the tube wall. As a consequence thereof, the outer layer of water changes to steam. During this process of changing to steam, the first change, which the outer layer of water undergoes, is the formation therein of steam bubbles. Mention has previously been made herein of the fact that steam bubbles act as an insulation. Consequently, unless the steam bubbles, which are being formed in the outer layer of water, are made to mix, they will, in essence remain stationary, i.e., stagnate, and take on the attributes of an insulative film, thereby causing localized hot spots to develop along the tube wall. Moreover, such hot spots, in turn, can cause overheating of the tube, and ultimately lead to tube failures. Additionally, unless they are made to mix, the steam bubbles, by virtue of their insulative capability, will also function to prevent further heating of the core of water, which is rapidly passing through the center of the tube in the form of laminar flow, the latter term being employed herein as defined above.
From the preceding discussion, it thus should now be readily apparent that in order to achieve the rapid and efficient transfer of heat through the tube walls to the water flowing therewithin, there exists a need to provide some form of means that would be operative to effect the breaking up of the laminar flow of water through the tube. Namely, some such form of means is needed to effect the mixing of the outer layer of water and thereby also the steam bubbles entrained therein with the core of water flowing in the central region of the tube. As noted previously one such form of means, which has been employed heretofore in the prior art, to achieve a controlled internal disruption of the flow of water through a boiler tube has involved the usage of ribbing, i.e., rifling, on the internal surface of the boiler tube.
Unfortunately, however, for the most part the boiler tubes that have been manufactured in accordance with the teachings of the prior art heretofore have been adversely characterized in the fact that they each have suffered from certain notable disadvantages. For example, a major disadvantage associated with boiler tubes produced by the methods and apparatus that have been known previously for effecting the formation of ribbed boiler tubes resides in the variableness of the rib design, which the boiler tube is made to embody. That is, there is an inherent inflexibility associated with virtually all of the methods and apparatus taught by the prior art insofar as concerns the matter of effectuating variations in the configuration of the rib design that is provided on the surface of the inner wall of a boiler tube.
Namely, as noted previously herein nucleate boiling can lead to the development of localized hot spots that, in turn, cause overheating and ultimately boiler tube failures. To minimize the establishment of such localized hot spots in boiler tubes stemming from the existence of nucleate boiling, it has been proposed by the prior art to provide ribbing, i.e., rifling, on the inner wall surface of the tube. Unfortunately, however, the methods and apparatus known in the prior art heretofore for effectuating the making of such rifle tubing render it difficult to enable significant variations in pattern configuration to be implemented for purposes of compensating for variations in the location of potential hot spots along the inner walls of the tubes. That is, most of the existing methods and apparatus are limited to the utilization of fixed patterns, such that each boiler tube, irrespective of the location it occupies in the boiler, i.e., its relative exposure to external sources of heat, is necessarily provided with the same pattern of rifling, even though from a heat transfer standpoint, it may be desirable to vary the pattern as between locations within the same tube, as well as between tubes in the same boiler.
By way of exemplification in this regard, particular attention is directed to U.S. Pat. No. 3,272,961, which issued to L. A. Maier, Jr., et al. on Sept. 13, 1966, and wherein a method and apparatus are taught for making rib vapor generating tubes. In accordance with the teachings of this patent a rib in a nature of a weld deposit is formed on the inside surface of a tube through the use of a welding process. The method and apparatus as taught therein, however, are disadvantageously characterized by their total lack of flexibility in effecting adjustments in the rifled pattern that is being formed in a boiler tube to compensate for providing the boiler tube with different heat transfer characteristics in various locations along the length thereof. Namely, in accord with the teachings of U.S. Pat. No. 3,272,961 the implementation of the formation of a rifled pattern in a tube is predicted upon the creation of a pattern that comprises a repeat of the same configuration for the entire length of each individual boiler tube. Moreover, not only are changes in pattern of rifling as between different locations in the same tube difficult to effect with the apparatus described in the aforesaid U.S. Pat. No. 3,272,961, but also, it is difficult therewith to effect changes in the pattern of rifling as between different tubes, wherein it is desired to have them embody individual heat transfer characteristics. Principally, this is because to effect such changes requires the establishment of completely different relationships between the components, i.e., tube, welding means, etc., from those which these components bear one to another in order to effectuate the formation in a boiler tube in a given rib design. That is, these components must have different relationships one to another for each different pattern of rifling, i.e., rib design, with which it is desired to provide a boiler tube.
Consequently, in order to effectuate the exercise of control over the motion of the fluid flowing through a boiler tube, the use of a variety of forms, shapes, sizes and/or patterns that are suitably provided on the inner surface of the tube is relied upon for this purpose. More specifically, such control is effected through the employment of means, which, for purposes of the discussion herein, is characterized by being a rib, irrespective of the shape which the latter may embody, or whether it is continuous or discontinuous. Most importantly, the exact configuration which such a rib formed on the surface of the tube bore is made to embody is a variable that is dependent upon the type of fluid medium, the fluid pressure, the fluid flow rate, the tube size, the temperature gradient within the tube wall in both a circumferential and a longitudinal direction, as well as other variables. A consideration of these factors for purposes of providing the inner tube wall with the physical characteristics that are required in order to ensure a proper fluid movement therein, so as to maximize the heat transfer rate to the fluid medium, can lead to the utilization of a rib design wherein the parameters applicable thereto are selected from variations that are possible in the angle that the ribbing bears to the lateral axis of the tube; variations which are possible in the spacing between individual ribs of the ribbing; whether the ribbing is continuous or discontinuous; whether the ribbing is provided on only one internal side wall of the tube or on more than one internal side wall thereof; and the particular dimensions of the rib in terms of the specific height, the specific width, the specific radii and the specific angles that individual portions of a given rib embodies.
By way of illustration in this regard, variations in the angle that the ribs bear to the lateral axis of the tube and/or variations in the spacing between individual ribs in a given rib design offer a high degree of flexibility in compensating for the potential existence of localized hot spots. As a case in point, through a selection of the proper parameters from the aforesaid variables, it is possible to establish a rib design wherein provision is made for the creation of the desired fluid flow properties for each increment of the length so as to effect a realization of the proper fluid movement for maximizing the heat transfer rate along the entire length of the tube. It is to be noted that for purposes of achieving a maximization of the heat transfer rate, it is conceivable that it could be deemed necessary to utilize a rib design wherein variations exist therein in each increment of the length. Apart from those types of variations mentioned at the outset of this paragraph, the need to obviate the existence of localized hot spots may also dictate the use of a rib design that is discontinuous, i.e., wherein the rib design is provided only in areas of the tube inner surface that are exposed to a high heat flux, and/or rib design that is provided on only one side wall of the tube, i.e., on the side wall of the tube that corresponds to the heat source side thereof. Finally, note is taken of the fact that various rib shapes may be employed. In this regard, the rib that is utilized may be symmetrical in shape while in other instances it may be deemed advisable to employ other rib shapes which offer directional flow features that can be advantageous to pressure drop considerations. Also, it is noted that the film coefficient of heat transfer can be improved through the proper selection of the shape of the rib inasmuch as the former is known to be dependent upon the direction of fluid flow relative to the heating surface. As with the spacing and the pitch of the ribs, the height, width, radii and angles of the various rib shapes can be controlled to fulfill predetermined design criteria. In conclusion, it has been recognized that each rib shape and rib side wall provide an individual flow motion and pressure drop, thereby offering an infinite range of fluid motion control from which for design purposes a selection can be had in order to provide the desired individual flow characteristics for each incremental section of a heat transfer system.
As has been mentioned previously hereinabove, a boiler tube embodying a rib design on its inner wall surface which meets the requirements for effecting the maximization of control over the movement of fluid therethrough forms the subject matter of copending patent application Ser. No. 73,967, which bears a filing date of Sept. 10, 1979, now U.S. Pat. No. 4,314,587. In accord with the teachings thereof, the particular configuration of rib design, which the ribbing embodies, is selected on the basis of the capability thereof to fulfill certain predetermined design criteria that are established by the need to provide the boiler tube with the proper fluid flow properties along each increment of its length. To this end, the parameters that define the nature of the ribbed design that is utilized are selected from amongst a plurality of variables. These variables encompass the following: the angle which the ribs of the ribbing bear to the transverse axis of the tube, i.e., the pitch of the ribbing; the spacing that exists between the individual ribs that collectively comprise the ribbing; whether the ribbing is continuous or discontinuous; whether the ribbing is located on one longitudinally side wall of the tube, or on more than one side wall thereof; and the shape that the individual ribs embody in terms of the height, width, radii and angles thereof.
Now as regards the subject matter of the present application, this application is directed to an electrical control circuit that is designed to be cooperatively associated with suitable welding means so as to be operative for purposes of providing a boiler tube with fluid flow control means of the type described and illustrated in copending patent application Ser. No. 73,967, now U.S. Pat. No. 4,314,587. More specifically, there is described and illustrated herein an electrical control circuit that is capable of being employed for purposes of effecting the application of a weld deposited rib on the wall surface of a boiler tube while concomitantly control is being exercised therewith over the size, pitch and pattern which the weld deposited rib embodies.
Thus, it is an object of the present invention to provide an electrical control circuit that is employable in cooperative association with welding means.
It is another object of the present invention to provide such an electrical control means which when cooperatively associated with welding means is capable of being employed for purposes of applying a weld deposited rib to the inner wall surface of a boiler tube.
It is still another object of the present invention to provide such an electrical control circuit which is operative to be used for purposes of applying a weld deposited rib to the inner surface of a boiler tube while concomitantly control is being exercised therewith over the nature of the rib being deposited.
A further object of the present invention is to provide such an electrical control circuit which is operative to be used for purposes of applying a weld deposited rib to the inner surface of a boiler tube while concomitantly control is being exercised therewith over the size of the rib being deposited.
A still further object of the present invention is to provide such an electrical control circuit which is operative to be used for purposes of applying a weld deposited rib to the inner surface of a boiler tube while concomitantly control is being exercised therewith over the pitch of the rib being deposited.
Yet another object of the present invention is to provide such an electrical control circuit which is operative to be used for purposes of applying a weld deposited rib to the inner surface of a boiler tube while concomitantly control is being exercised therewith over the continuousness of the rib being deposited.
Yet still another object of the present invention is to provide such an electrical control circuit which is operative to be used for purposes of applying a weld deposited rib to the inner surface of a boiler tube while concomitantly control is being exercised therewith over the spacing of the rib being deposited.
Yet a further object of the present invention is to provide such an electrical control circuit which is advantageously characterized by the fact that it is relatively inexpensive to provide, and relatively easy to utilize.